Digital representation, storage, distribution, and duplication of digital media have become very popular because they are inexpensive, easy to use, and maintain the quality of the media. These advantages however have enabled widespread, illegal distribution and use of copyrighted material, such as unauthorized distribution of digital images and videos over the Internet, for example. As a result, the rightful copyright owners are deprived of their revenues.
One group of technologies that can be deployed to control that unauthorized distribution involves embedding imperceptible information in a video. These technologies are often referred to as digital watermarking, forensic marking or video marking and these terms are used interchangeably in this text. The embedded information can be used to embed the identity of the copyright owner, distributor, or recipient of the media in a secure, imperceptible and robust fashion. The information can, for example, be embedded during playback or reception by an individual, and relate to the time of reception and the individual recipient by means of an identification number. If the copy is later found distributed illegally, the information can be retrieved and the original recipient, who is responsible for the illegal distribution can be identified. This technology can be used for tracking of individual media asset copies and enforcement of copyright laws. Content marking is an important component of digital media distribution and enables digital delivery of copyright protected content by limiting the risk of illegal distribution e.g., through peer to peer file sharing sites. Because the distribution can be tracked to the last legal recipient, the risk of being held responsible for copyright violations increases, as the person distributing the content can be identified.
While the tracking number can be embedded using obvious and visible modifications, they are less destructive to the content and better secured against removal, if applied in an invisible fashion.
In order to apply a robust mark (i.e., the mark remains readable after the content has been modified through compression, re-recording, filtering or other processes), changes to the content have to be applied that modify the actual video, image, or audio signal. For the mark to remain imperceptible, these modifications are applied in a hidden and slight manner.
In order to archive the required robustness, the modifications are typically applied in a distributed fashion, with numerous modifications spread over a large area of a video frame or time (i.e., over a number of frames), or both. Often, the manipulations are applied in a transformed domain, such as a frequency or wavelet transformation. These transformations allow for invisible marking modifications in a domain that remains largely intact after modifications to the video, and allows aggregation of modifications that are distributed over a number of frames when the media is observed. These transformations also enable a strong signal in a transformed domain to be embedded. The signal is largely imperceptible in the domain that is used to present the media to the user.
The number of modifications required for embedding the mark, and the number of calculations required to transform the content in the domain where the content can be marked, pose a challenge for processing in environments where fast and efficient embedding of a mark is required. An example of such an environment is an environment that employs streaming media, which delivers a media to a consumer electronics device via a network.
When embedding information about the recipient of the streaming/transmitted media, the information can be embedded at the receiving end, so that the sender is not burdened with marking and sending individual streams for every recipient. The sender delivers the identical media copy to all recipients and the media is marked at the time it is received at the recipient's end. Thereafter, each user is presented with a copy that is individually marked. In this scenario, the limitation of timely processing is even greater, since the machine on the receiving end often has very limited processing power available to apply the mark. This limitation of processing power makes it prohibitive to apply forensic marks that contain information about the recipient in media in most distribution environments in use today.